Fluoro Brite is a twisted fluorescent thread. To get it to lay perfectly flat simply untwist with your bobbin holder and then it can be used as a flat floss and it has the most vibrant UV which the fish will find irresistible.
Fluoro Brite was designed to be different. Since Joseph Keen's book "Fluorescent Flies" and Thomas Clegg's "The Truth About Fluorescents", fly tyers have been working with fluorescent materials and Semperfli decided to make a fluorescent thread with advantages that it could be used as a tying thread or as a floss.
Fluoro Brite has been specially formulated for fluorescence and comes in 240 denier (3/0). It is recommended for hooks 10 to 2/0 but if you want to use it for smaller flies, Fluoro Brite will split down further. Use it as a hotspot, for ribbing, a body or even a fab hot spot tail. For tails we fold Fluoro Brite four times in a loop and tie it in the tail of a fly, cut to length then tease the fibres apart with a dubbing brush to get an astounding crinkled tail.
What is well known is that fluorescent materials do attract trout, salmon and other species. We cannot see material effects except under a UV torch where we see the glow. But with their visual rods and cones capable of seeing into the UV spectrum many fish species see this like a light in the dark.
Fluorescent materials work well one hour before daylight and one hour after nightfall, because even though we cannot see them, UV rays from the sun still hit the water and ignite your flies.
25m (approx) per spool.